“Lots of different reasons,” she said, “but it just comes down to my personal choice for each.”

State health officials said most measles cases in the US involve people who have not been vaccinated that were exposed to infected travelers coming into the country.

“Our public health challenge is to make sure everyone who is around that person is vaccinated,” said Dr. Paul Cieslak, the manager of the Acute & Communicable Disease Prevention Section at the Oregon Public Health Division.